Thrusting devices for rolling mills

ABSTRACT

A thrusting device for rolling mills, comprising an electric resetting mechanism in which the position of rolls is fed back by directly electrically detecting a movement of a thrusting ram received in a hydraulic cylinder for adjusting an amount of stroke of rolls relative to each other.

I United States Patent 1 1 1111 3,736,782

Fu'ino et al. 1 June 5 1973 541 THRUSTING DEVICES FOR ROLLING 3,566,638 3/1971 Herbst ..72 s MILLS 3,326,028 6 1967 Kajiwara ..72/245 3,568,484 3/1971 Bond etal. ..72 8 1 lnventOYsI l Toshlyukl 3,570,288 3/1971 Fisher et al ..72/s Kallwal'aiboth OfHIIaChIJaPaH 3,546,908 12/1970 Russell ....72/21 73 Assignee: HitachiLtd. Tokyojapan 3,075,417 1/1963 Blain ..72/8

[22] Filed: 1970 Primary Examiner-Richard J. Herbst [21] Appl. No.2 82,277 Attorney-Craig, Antonelli & Hill [30] Foreign Application Priority Data [57] ABSTRACT Oct 22 1969 M an 44/83895 A thrusting device for rolling mills, comprising an p electric resetting mechanism in which the position of 52 U.S. c1 ..72/:; 72/245 mus is fed back by directly electrically detecting a 51 1m. 01. 321 15 37/08 movement of a thrusting Yam received in a hydraulic 581 Field of Search ..72/s,21,245 Cylinder for adjusting an amount of Stroke of rolls relative to each other.

[56] References Cited UNITED STATES PATENTS 8 Claims, 3 Drawing Figures 3,559,432 2/1971 Rastelli ..72/i9 PILOT The present invention relates to a thrusting device for rolling mills in which an amount of stroke of rolls relative to each other is adjustable by means of a hydraulic cylinder.

Thrusting devices of the type described which have been used heretofore, include electrically driven types and hydraulically driven types. The former is so designed that an amount of stroke of rolls is adjusted by thrusting screws which are rotated from an electric motor through a reduction gearing, worms and worm wheels, and, therefore, has the disadvantages that the power transmission efficiency is poor due to the excessively great reduction ratio and the use of a screw mechanism, that an electric motor of large capacity and a bulky speed reduction mechanism are required for the thrusting operation, adding to the cost of the rolling mills, and further that the maintenance and inspection of the device are cumbersome. On the other hand, the latter is composed of a hydraulic cylinder, a pilot valve and drive means for actuating the piston of the pilot valve, and does not require a sizable thrusting mechanism such as is used in the electrically driven type, so that it is extremely simple in construction and can be manufactured at low cost as compared with the former. In the conventional thrusting devices of hydraulically driven type, however, since the piston of the pilot valve is adjusted either directly by hand or some driving means, it is difficult to effect a parallel movement of the rolls relative to each other clue to varying load conditions and different fluid resistances and hence it is impossible to give a proper amount of stroke thereto. For this reason, the rolling mill with the conventional thrusting device of hydraulically driven type has been used only for a rolling operation such as of aluminum foils in which the thickness of blanks is quite small as compared with the diameter of rolls and any interroll clearance is not set prior to the rolling operation.

Under the circumstances, the present inventor has previously proposed an improved thrusting device as disclosed in U.S. Pat. No. 3,326,028.

This prior invention is an epoch-making one which has made possible the practical use of a hydraulically operative thrusting device in cold strip mills for the first time in the world, but the only shortcoming of the thrusting device is that it comprises complicated mechanical resetting means to effect a return movement of the rolls. in such mechanical resetting means, a clearance between and elastic deformation of the component parts are inevitable, which will become progressively large during use of the resetting means over an extended period, not only rendering the maintenance and inspection procedures cumbersome but also giving an adverse effect on the operational accuracy and the response speed of the system.

Further, the roll stand must be coupled with a control system either mechanically or by way of a hydraulic system, and such control system has to be provided close to the roll stand in the case where the hydraulic system is employed for the coupling, not speaking of the case where the control system is coupled with the roll stand mechanically, because the hydraulic system includes a piping which must be completely sealed fluid-tightly. On the other hand, a control system including mechanical resetting means is large in size and requires a wide space for installation. However, such a wide space is usually not available in the vicinity of the roll stand in the present situation in which a difficulty is being encountered even in providing a space for the installation of the other necessary equipments.

in U.S. Pat. No. 3,075,417, there is disclosed an apparatus in which a movement of a ram of a hydraulically operative thrusting device and a movement of a separate plunger operable under the pressure in a hydraulic cylinder are balanced by means of a leaf spring and the position of a hydraulic pressure regulating pilot valve is determined by the balanced position of said leaf spring. This apparatus, however, lacks a transient stability due to the use of the spring and the plunger which undergoes the influence of a force of inertia. Furthermore, since a feed back mechanism is provided in the vicinity of the thrusting ram where the working fluid and scale drop, this prior art apparatus not only has the same disadvantages as described above but also involves problems in the operational stability and mainvtenance of the facility. An additional disadvantage of the apparatus is that the parallelism in the movement of the left and right portions of a roll cannot be maintained positively.

The present invention has been achieved to deal with such problems as described above.

Namely, an object of the present invention is to provide a thrustingdevice for rolling mills, which is provided with electric resetting means which renders the thrusting device highly responsive to an instruction, is operative with high accuracy and easy in maintenance and inspection, requires a less space for installation and can be easily moved from place to place as required.

Another object of the invention is to provide a thrusting device for rolling mills, in which thrusting means on the driving side and thrusting means on the operating side are operatively associated with each other to ensure that the movement of the left and right portions of a roll is maintained parallel.

A characteristic feature of the present invention resides in the fact that a hydraulically operative thrusting device is controlled by a combination of means for detecting the position of the rolls (hereinafter referred to as roll position detecting means) by directly detecting a movement of a ram in a hydraulic cylinder and an electric control system utilizing the output of said roll position detecting means. Another feature of the invention resides in the fact that an intermediate cylinder having a diameter smaller than that of a hydraulic cylinder is provided in addition to said hydraulic cylinder, and a hydraulically operative thrusting device is controlled by a combination of roll position detecting means which converts a movement of a piston in said intermediate cylinder into an electric signal and an electric control system utilizing the output of said roll position detecting means. Still another feature of the invention resides in the fact that a feed back signal from one side is fed to a control operator on the other side, together with a feed back signal from the other side and a thrusting instruction for the other side is controlled in such a manner that both feed back signals become equal.

The present invention will be described in detail hereinafter by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of an embodiment of the thrusting device for rolling mills according to the present invention;

FIG. 2 is a schematic view similar to FIG. 1 but showing another embodiment of the thrusting device of the invention; and

FIG. 3 is a schematic view showing the connection between the driving side and the operating side of the thrusting device shown in FIG. 2.

Referring to the drawings, reference numeral 1 designates a roll housing; 2, 3 working rolls; 4, 5 backing rolls; 6, 7 working roll metal chocks; 8, 9 backing roll metal chocks; 10 working roll balancing means; 12 a thrusting ram; and 13 a cylinder. The rolls 3, 5 are moved up and down by a vertical movement of the thrusting ram 12. Reference numeral 14 designates a rod having one end connected to the thrusting ram 12, with the other end extending downwardly through the bottom of the cylinder l3; 15 a rack provided on the rod 14; 16 a pinion in meshing engagement with the rack 15; and 17 a detector to be driven by the pinion 16 to detect the position of the thrusting ram 12, Le. the lowered positions of the rolls, and emits a signal according to the detected position. As will be clear from the illustrations, the detector 17 practically consists of a rotary speedmeter adapted to directly detect a movement of the thrusting ram 12. Reference numeral 18 designates a comparator which compares a thrusting instruction S and the signal from said detector with each other and produces an output where there is a difference therebetween, Le. a control operator including an amplifier. Reference numeral 19 designates a pilot valve to control the flow rate of fluid in proportion to the amount of an electrical instruction from the comparator 18; 20 a pump for feeding hydraulic pressure; 21 a stop valve; 22 a directional control valve; 23 27 fluid conduits; and 28 a fluid tank.

The thrusting devices of the invention shown in the drawings of course include an accumulator and a relief valve such as are used in the ordinary hydraulic system, though not apparent in the drawings. Further, the stop valve 21, the directional control valve 22 and the fluid conduits 25 and 27 are not used in the normal rolling operation but used for the adjustment of the opening degree of rolls only on replacement of the rolls, and will not be described in detail herein.

In the thrusting devices of the construction described above, the stop valve 21 is held in a closed position and the thrusting ram 12 is operated only by the pilot valve 19, in the rolling operation. When it is intended to press the lower working roll 3 toward the upper working roll 2, an electric signal corresponding to the thrusting instruction S is given to the pilot valve 19 and an amount of fluid corresponding to said electric signal is fed into the cylinder 13 through the conduit 23, whereby the thrusting ram 12 is moved upward to effect a desired reduction. On the other hand, the movement of the thrusting ram 12 is transmitted to the detector 17 through the rod 14, the rack 15 and the pinion 16, and an electric signal emitted from said detector 17 is fed back to the comparator 18. In the comparator, the electric signal from the detector 17 is compared with the value of the initially given instruction S. The comparator 18 produces an output until the stroke of the lower working roll 3 reaches a preset value and the operation of the pilot valve 19 is controlled by said output. Thus, the position of the lower working roll 3 is maintained accurately according to the preset value.

In the thrusting device of FIG. 2, an intermediate cylinder 30, smaller in diameter than the cylinder 13, is interposed between the thrusting ram 12 and the pilot valve 19, and a piston received in said cylinder 30 is operated by pressurized fluid supplied into said cylinder 30 from the pilot valve 19 through a conduit 33, whereby pressurized fluid is fed into the cylinder 13 through a conduit 34.

In this embodiment, the lower roll position detecting rack 15 is provided on a piston rod 32 of the intermediate cylinder 30 and the pinion 16 is in meshing engagement with said rack 15. The other construction is identical with that of the embodiment of FIG. 1.

The conduit 34 communicating the intermediate cylinder 30 with the cylinder 13 is completely sealed against fluid leakage, so that the movement of the thrusting ram 12 is amplified into the movement of the piston 31 in the intermediate cylinder 30 with no delay at all, which will be detected by the detector 17. The subsequent operation of the device is exactly identical with that of the embodiment shown in FIG. 1. v

In the operation described above, the feed back system composed of the detector 17 and the comparator l8 converts the movement of the thrusting ram 12 into an electric signal, either directly or after amplifying it into the movement of the piston 31 in the intermediate cylinder 30, and compares the electric signal with the value of the thrusting instruction, as contrasted to the mechanical resetting means. Therefore, no delay occurs in the feed back system as well as in the detecting portion, and a deviation between the compared values can be directly transmitted to the pilot valve 19 after being amplified. The roll positions can be detected particularly easily and with high accuracy in case of the arrangement of FIG. 2, since an extremely small movement of the thrusting ram 12 is amplified into a movement of the piston 31 in the intermediate cylinder 30 which is smaller in diameter than the cylinder 13.

Owing to the complete fluid-tight sealing of the fluid conduits as stated above, the detector 17 can detect the movement of the thrusting ram 12 with the same accuracy as obtainable when it directly detects the same. Therefore, a fluid leakage, if any, in the hydraulic driving system will not make the detected value erroneous and a deviation obtained represents a true deviation between the detected value and the value of the instruction, similar to the case of the embodiment shown in FIG. 1. The same thing can be said on any and all errorinducing factors involved in driving the thrusting ram 12 and the intermediate cylinder 30, and such meritorious feature makes the highly accurate positioning of the rolls possible. According to the present invention, the operation of the thrusting device is controlled such that the movement of the thrusting ram 12 becomes equal to the value of instruction per. se. as stated above. From the standpoint of accuracy, therefore, the operation of the thrusting device is not adversely affected by a lack of accuracy of the hydraulic driving system proper but depends solely upon the accuracy of the detector 17. However, there is no problem in this respect since a highly accurate converter for converting a mechanical displacement into an electric signal has been well known in the art.

Further, according to the present invention there can be obtained the remarkable practical advantages that the thrusting device can be constructed simply in a compact form and can be maintained and inspected very easily, and further it can be positioned at any desired location by employing an electric wiring for coupling it with the roll stand.

FIG 3 shows an arrangement wherein two thrusting devices of the type shown in FIG. 2, each on each of the driving side and the operating side, are operatively connected with each other so that a more positive parallel movement of the left and right rolls may be obtained.

In FIG. 3, reference numerals l9 and 30 34 designate the same elements as those indicated by the same reference numerals in FIG. 2 respectively, of the thrusting device, for example, on the operating side of the rolling mill, and reference numerals 15 19' and 30' 34' designate the same elements as those indicated by numerals 15 19 and 30 34 respectively, of the thrusting device on the driving side. Reference numeral 35 designates a change-over switch provided midway of a line through which the signal from the detector 17 is transmitted to the comparator 18'. Reference characters V, V designate the signals from the detectors 17, 17' respectively; and S, S designate thrusting instruction signals to be given to the operating side and the driving side respectively.

When it is intended to thrust the left and right portions of rolls concurrently, the change-over switch 35 is closed and the signals S and S, which is the same as the signal S, are given to the comparators 18, 18' of the respective thrusting devices respectively. As a result, the pilot valves 19, 19' are opened and the pistons 31, 31' in the respective intermediate cylinders 30, 30' are operated by the fluid supplied through said respective pilot valves and thus the signals V, VI from the detectors 17, 17 are fed back to the comparators 18, 18' respectively. In this case, the pilot valve 19 is given an instruction to make V equal to S in the comparator 18, but the pilot valve 19' is given an instruction to make V equal to V in the comparator 18. Thus, the rolls on the operating side and the driving side can be moved in parallel relation to each other positively.

We claim:

1. An arrangement for adjusting the spacing between working rolls in a rolling mill comprising: first hydraulic cylinder-piston means having a first piston and a first cylinder linearly displaceable with respect to one another, one of said first cylinder and first piston being connected to one of the working rolls of the rolling mill such that said one working roll is moved linearly with respect to another working roll by said first cylinderpiston means the same distance as the relative displacement of said first piston and first cylinder, a ram operatively connected to said one of said first cylinder and first piston for linear movement therewith, hydraulic pressure supply means for supplying hydraulic pressure to said first cylinder-piston means to effect relative displacement of said first cylinder and first piston, pilot valve means arranged in said supply means for directly controlling the hydraulic pressure supplied to the first cylinder-piston means, detecting means including converting means for converting linear movement of said ram directly into a corresponding first electrical signal, said converting means including means for converting the linear movement of the ram into rotational movement of a rotatable member and means for converting the angular displacement of said rotatable member into said first electrical signal, means for supplying a second electrical signal representing a predetermined desired spacing of said working rolls, and electrical comparator means connected to both of said first and second electrical signals and including means for providing an electrical output control signal corresponding to the difference in said first and second electrical signals, said output control signal being directly connected to said pilot valve means for controlling said pilot valve means, whereby the adjusting movement of said one working roll by said first piston-cylinder means corresponds directly to the detected position of said one working roll.

2. An arrangement according to claim 1, wherein said ram is rigidly fixed to said one of said first cylinder and first piston.

3. An arrangement according to claim 1, wherein said working rolls are arranged for relative spacing movement with respect to one another in a housing, wherein said first cylinder is fixed to said housing, and wherein said piston is movable along with said one working roll.

4. An arrangement for adjusting the spacing between working rolls in a rolling mill comprising: first hydraulic cylinder-piston means having a first piston and a first cylinder linearly displaceable with respect to one another, one of said first cylinder and first piston being connected to one of the working rolls of the rolling mill such that said one working roll is moved linearly with respect to another working roll by said first cylinderpiston means the same distance as the relative displacement of said first piston and first cylinder, a ram operatively connected to said one of said first cylinder and first piston for linear movement therewith, hydraulic pressure supply means for supplying hydraulic pressure to said first cylinder-piston means to effect relative displacement of said first cylinder and first piston, pilot valve means arranged in said supply means for directly controlling the hydraulic pressure supplied to the first cylinder-piston means, detecting means including means for converting linear movement of said ram directly into a corresponding first electrical signal, means for supplying a second electrical signal representing a predetermined desired spacing of said working rolls, and electrical comparator means connected to both of said first and second electrical signals and including means for providing an electrical output control signal corresponding to the difference in said first and second electrical signals, said output control signal being directly connected to said pilot valve means for controlling said pilot valve means, whereby the adjusting movement of said one working roll by said first pistoncylinder means corresponds directly to the detected position of said one working roll, wherein said working rolls are arranged for relative spacing movement with respect to one another in a housing, wherein said first cylinder is fixed to said housing, wherein said piston is movable along with said one working roll, and wherein said ram is rigidly fixed to said first piston, wherein a toothed rack is provided on a portion of said ram extending out of said first cylinder, and wherein said detecting means includes a toothed wheel directly engaging said toothed rack.

5. An arrangement for adjusting the spacing between working rolls in a rolling mill comprising: first hydraulic cylinder-piston means having a fist piston and a first cylinder linearly displaceable with respect to one another, one of said first cylinder and first piston being connected to one of the working rolls of the rolling mill such that said one working roll is moved linearly with respect to another working roll by said first cylinderpiston means the same distance as the relative displacement of said first piston and first cylinder, a ram operatively connected to said one of said first cylinder and first piston for linear movement therewith, hydraulic pressure supply means for supplying hydraulic pressure to said first cylinder-piston means to effect relative displacement of said first cylinder and first piston, pilot valve means arranged in said supply means for directly controlling the hydraulic pressure supplied to the first cylinder-piston means, detecting means including convetting means for converting linear movement of said ram directly into a corresponding first electrical signal, means for supplying a second electrical signal representing a predetermined desired spacing of said working rolls, and electrical comparator means connected to both of said first and second electrical signals and including means for providing an electrical output control signal corresponding to the difference in said first and second electrical signals, said output control signal being directly connected to said pilot valve means for controlling said pilot valve means, whereby the adjusting movement of said one working roll by said first piston-cylinder means corresponds directly to the detected position of said one working roll, wherein a second piston-cylinder means having a second piston and second cylinder is arranged in said hydraulic pressure supply means between said first piston-cylinder means and said detecting means, said second piston-cylinder means being in operative communication with said first piston-cylinder means solely by way of a closed hydraulic conduit such that relative displacement of the respective pistons and cylinders of the first and second piston-cylinder means are directly linearly correlated to one another, wherein said ram is rigidly fixed to one of said second piston and second cylinder, and wherein said converting means includes means for converting the linear movement of the ram into rotational movement of a rotatable member and means for converting the angular displacement of said rotatable member into said first electrical signal.

6. An arrangement for adjusting the spacing between working rolls in a rolling mill comprising: first hydraulic cylinder-piston means having a first piston and a first cylinder linearly displaceable with respect to one another, one of said first cylinder and first piston being connected to one of the working rolls of the rolling mill such that said one working roll is moved linearly with respect to another working roll by said first cylinderpiston means the same distance as the relative displacement of said first piston and first cylinder, a ram operatively connected to said one of said first cylinder and first piston for linear movement therewith, hydraulic pressure supply means for supplying hydraulic pressure to said first cylinder-piston means to effect relative displacement of said first cylinder and first piston, pilot valve means arranged in said supply means for directly controlling the hydraulic pressure supplied to the first cylinder-piston means, detecting means including means for converting linear movement of said ram directly into a corresponding first electrical signal, means for supplying a second electrical signal representing a predetermined desired spacing of said working rolls, and electrical comparator means connected to both of said first and second electrical signals and including means for providing an electrical output control signal corresponding to the difference in said first and second electrical signals, said output control signal being directly connected to said pilot valve means for controlling said pilot valve means, whereby the adjusting movement of said one working roll by said first pistoncylinder means corresponds directly to the detected position of said one working roll, wherein a second pis-- ton-cylinder means having a second piston and second cylinder is arranged in said hydraulic pressure supply means between said first piston-cylinder means andsaid detecting means, said second piston-cylinder means being in operative communication with said first piston-cylinder means solely by way of a closed hydraulic conduit such that relative displacement of the respective pistons and cylinders of the first and second piston-cylinder means are directly linearly correlated to one another, and wherein said ram is rigidly fixed to the second piston, wherein the second cylinder is fixed with respect to said first cylinder, wherein a toothed rack is provided on a portion of said ram extending out of said second cylinder, and wherein said detecting means includes a toothed wheel directly engaging said toothed rack.

7. An arrangement according to claim 6, wherein said closed hydraulic conduit communicates a first surface of the first piston directly with a first surface of the second piston, and wherein the variable pressure supply controlled by the pilot valve communicates directly with a second surface of the second piston which faces oppositely from said first surface.

8. An arrangement according to claim 7, wherein the first surface of the first piston is larger than the first surface of the second piston whereby linear movements of said one working roll are amplified by said second pis- 

1. An arrangement for adjusting the spacing between working rolls in a rolling mill comprising: first hydraulic cylinderpiston means having a first piston and a first cylinder linearly displaceable with respect to one another, one of said first cylinder and first piston being connected to one of the working rolls of the rolling mill such that said one working roll is moved linearly with respect to another working roll by said first cylinder-piston means the same distance as the relative displacement of said first piston and first cylinder, a ram operatively connected to said one of said first cylinder and first piston for linear movement therewith, hydraulic pressure supply means for supplying hydraulic pressure to said first cylinder-piston means to effect relative displacement of said first cylinder and first piston, pilot valve means arranged in said supply means for directly controlling the hydraulic pressure supplied to the first cylinder-piston means, detecting means including converting means for converting linear movement of said ram directly into a corresponding first electrical signal, said converting means including means for converting the linear movement of the ram into rotational movement of a rotatable member and means for converting the angular displacement of said rotatable member into said first electrical signal, means for supplying a second electrical signal representing a predetermined desired spacing of said working rolls, and electrical comparator means connected to both of said first and second electrical signals and including means for providing an electrical output control signal corresponding to the difference in said first and second electrical signals, said output control signal being directly connected to said pilot valve means for controlling said pilot valve means, whereby the adjusting movement of said one working roll by said first piston-cylinder means corresponds directly to the detected position of said one working roll.
 2. An arrangement according to claim 1, wherein said ram is rigidly fixed to said one of said first cylinder and first piston.
 3. An arrangement according to claim 1, wherein said working rolls are arranged for relative spacing movement with respect to one another in a housing, wherein said first cylinder is fixed to said housing, and wherein said piston is movable along with said one working roll.
 4. An arrangement for adjusting the spacing between working rolls in a rolling mill comprising: first hydraulic cylinder-piston means having a first piston and a first cylinder linearly displaceable with respect to one another, one of said first cylinder and first piston being connected to one of the working rolls of the rolling mill such that said one working roll is moved linearly with respect to another working roll by said first cylinder-piston means the same distance as the relative displacemEnt of said first piston and first cylinder, a ram operatively connected to said one of said first cylinder and first piston for linear movement therewith, hydraulic pressure supply means for supplying hydraulic pressure to said first cylinder-piston means to effect relative displacement of said first cylinder and first piston, pilot valve means arranged in said supply means for directly controlling the hydraulic pressure supplied to the first cylinder-piston means, detecting means including means for converting linear movement of said ram directly into a corresponding first electrical signal, means for supplying a second electrical signal representing a predetermined desired spacing of said working rolls, and electrical comparator means connected to both of said first and second electrical signals and including means for providing an electrical output control signal corresponding to the difference in said first and second electrical signals, said output control signal being directly connected to said pilot valve means for controlling said pilot valve means, whereby the adjusting movement of said one working roll by said first piston-cylinder means corresponds directly to the detected position of said one working roll, wherein said working rolls are arranged for relative spacing movement with respect to one another in a housing, wherein said first cylinder is fixed to said housing, wherein said piston is movable along with said one working roll, and wherein said ram is rigidly fixed to said first piston, wherein a toothed rack is provided on a portion of said ram extending out of said first cylinder, and wherein said detecting means includes a toothed wheel directly engaging said toothed rack.
 5. An arrangement for adjusting the spacing between working rolls in a rolling mill comprising: first hydraulic cylinder-piston means having a fist piston and a first cylinder linearly displaceable with respect to one another, one of said first cylinder and first piston being connected to one of the working rolls of the rolling mill such that said one working roll is moved linearly with respect to another working roll by said first cylinder-piston means the same distance as the relative displacement of said first piston and first cylinder, a ram operatively connected to said one of said first cylinder and first piston for linear movement therewith, hydraulic pressure supply means for supplying hydraulic pressure to said first cylinder-piston means to effect relative displacement of said first cylinder and first piston, pilot valve means arranged in said supply means for directly controlling the hydraulic pressure supplied to the first cylinder-piston means, detecting means including converting means for converting linear movement of said ram directly into a corresponding first electrical signal, means for supplying a second electrical signal representing a predetermined desired spacing of said working rolls, and electrical comparator means connected to both of said first and second electrical signals and including means for providing an electrical output control signal corresponding to the difference in said first and second electrical signals, said output control signal being directly connected to said pilot valve means for controlling said pilot valve means, whereby the adjusting movement of said one working roll by said first piston-cylinder means corresponds directly to the detected position of said one working roll, wherein a second piston-cylinder means having a second piston and second cylinder is arranged in said hydraulic pressure supply means between said first piston-cylinder means and said detecting means, said second piston-cylinder means being in operative communication with said first piston-cylinder means solely by way of a closed hydraulic conduit such that relative displacement of the respective pistons and cylinders of the first and second piston-cylinder means are directly linearly correlated to one another, wherein said ram is rigidly fixed to one of said second piston and second cylinder, and wherein said converting means includes means for converting the linear movement of the ram into rotational movement of a rotatable member and means for converting the angular displacement of said rotatable member into said first electrical signal.
 6. An arrangement for adjusting the spacing between working rolls in a rolling mill comprising: first hydraulic cylinder-piston means having a first piston and a first cylinder linearly displaceable with respect to one another, one of said first cylinder and first piston being connected to one of the working rolls of the rolling mill such that said one working roll is moved linearly with respect to another working roll by said first cylinder-piston means the same distance as the relative displacement of said first piston and first cylinder, a ram operatively connected to said one of said first cylinder and first piston for linear movement therewith, hydraulic pressure supply means for supplying hydraulic pressure to said first cylinder-piston means to effect relative displacement of said first cylinder and first piston, pilot valve means arranged in said supply means for directly controlling the hydraulic pressure supplied to the first cylinder-piston means, detecting means including means for converting linear movement of said ram directly into a corresponding first electrical signal, means for supplying a second electrical signal representing a predetermined desired spacing of said working rolls, and electrical comparator means connected to both of said first and second electrical signals and including means for providing an electrical output control signal corresponding to the difference in said first and second electrical signals, said output control signal being directly connected to said pilot valve means for controlling said pilot valve means, whereby the adjusting movement of said one working roll by said first piston-cylinder means corresponds directly to the detected position of said one working roll, wherein a second piston-cylinder means having a second piston and second cylinder is arranged in said hydraulic pressure supply means between said first piston-cylinder means and said detecting means, said second piston-cylinder means being in operative communication with said first piston-cylinder means solely by way of a closed hydraulic conduit such that relative displacement of the respective pistons and cylinders of the first and second piston-cylinder means are directly linearly correlated to one another, and wherein said ram is rigidly fixed to the second piston, wherein the second cylinder is fixed with respect to said first cylinder, wherein a toothed rack is provided on a portion of said ram extending out of said second cylinder, and wherein said detecting means includes a toothed wheel directly engaging said toothed rack.
 7. An arrangement according to claim 6, wherein said closed hydraulic conduit communicates a first surface of the first piston directly with a first surface of the second piston, and wherein the variable pressure supply controlled by the pilot valve communicates directly with a second surface of the second piston which faces oppositely from said first surface.
 8. An arrangement according to claim 7, wherein the first surface of the first piston is larger than the first surface of the second piston whereby linear movements of said one working roll are amplified by said second piston. 